Optimized protocols for sperm cryopreservation and in vitro fertilization in the rat

Laboratory rats have been used in biomedical research for over 170 years. Recently, genome editing technology has facilitated the generation of genetically modified rats worldwide. This development has increased the demand for efficient preservation and production of rat resources. Sperm cryopreservation is the most efficient and robust means to archive genetic resources, and this technique reduces the number of animals required for colony management. Previously, we have reported a protocol for rat sperm cryopreservation and in vitro fertilization using frozen-thawed sperm. Here we describe an improved in vitro fertilization protocol to enhance the fertilization rate of cryopreserved sperm in major strains of rats. In this optimized protocol, treatment of frozen-thawed rat sperm with a high concentration of bovine serum albumin (40 mg/ml) results in a high in vitro fertilization rate. This protocol consists of three main steps: preparation of cryopreserved sperm, in vitro fertilization using cryopreserved sperm and embryo transfer. This process takes approximately 1 month to produce live pups from cryopreserved sperm. This protocol can be easily implemented by researchers and technicians with experience in reproductive engineering technology; it can also be used, albeit with some practice, by researchers and technicians who have no experience in reproductive techniques. This sperm cryopreservation and in vitro fertilization protocol for rats will provide an efficient system for the archiving and production of genetically modified rats for the transgenic community.